This invention relates generally to the methods and systems for detection of very small amount of chemicals (trace chemicals) by employing light scattering probes. More particularly, this invention relates to an improved light scattering probe and a chemical sensor.
Despite the fact Raman detectors have sensitivity down to a level of single molecule detection (SMD), due to several technical difficulties; conventional Raman sensors still have very limited applications. Specifically, one of the major limitations of Raman spectroscopy application is the weak Raman scattering signal for trace chemical detection. There are many efforts in attempt to resolve this problem of low scattering signals in the field of Raman sensing. However, such efforts still have very limited success and have not been able to make Raman detectors available for practical and economical applications that urgently require ultra sensitive chemical trace detections.
Roughened or nano-structured sensing surface is known to generate strong scattering signals. Specifically, the nano-structured materials have found numerous applications in sensing, bioscience, materials science, semiconductor, etc. One of the promising applications of sensing technologies with nano-structured materials is Surface-Enhanced Raman Spectroscopy (SERS) and Surface-Enhanced Resonance Raman Spectroscopy (SERRS). It has been discovered that the Raman scattering signal can be enhanced by 104˜1014 times when molecules are adsorbed on a nano-structured noble metal (such as Ag Au and Cu, but not limited to Ag, Au and Cu) surface compared to normal Raman scattering. Specially, Raman scattering signal gets remarkably enhanced if the surface nanoparticles are isolated. The enhancement is determined by several factors, among them, the dimensions of the nano-particles and the distance among these nanoparticles on the surface are very important. It is found that as the scale of these nanoparticles decreases, the signal enhancement of Raman scattering increases. Further, as the distance between neighboring nanoparticles islands varies, the enhancement effect of Raman scattering also varies. However, the conventional technologies, for example, VLSI lithography technology, are still encountered with technical difficulties to fabricate nano-structure surfaces with reduced dimensions of the nano-particles and reduced distance among these nano-particles on the surface to achieve scattering signal enhancement.
The very limited availability of non-contaminated nano-structured noble metal surface is still a major difficulty faced by those of ordinary skill of the art in applying the technologies of SERS (Surface-Enhanced Raman Scattering) and SERRS (Surface-Enhanced Resonant Raman Scattering) for trace chemical detection. A non-contaminated nano-structured noble metal surface is required to conveniently deploy in the field for molecular adsorption and subsequent measurement. Due to this limit availability, even though the detection of trace chemicals can be achieved a part-per-billion (ppb) level, the techniques of applying SERS and SERRS for detecting trace of explosives and/or other chemical materials still have very limited applications.
The technologies of applying SERS and SERRS for detecting trace chemicals were described in many published papers such as “Probing Single Molecules And Single Nanoparticles by Surface Enhanced Raman Scattering”, Shuming Nie and Steven R. Emory, Science, 1997, 275, 1102-1106; “Surface Enhanced Raman Spectroscopy of Individual Rhodamine 6G Molecules on Large Ag Nanocrystals”, Amy M Michaels, M. Nirmal, and L. E. Brus. J. Am. Chem. Soc. 1999, 121, 9932-9939; “Single Molecule Detection Using Surface-Enhanced Raman Scattering (SERS)”, Katrin Kneipp, Yang Wang, Harald Kneipp, Lev L. Perelman, Irving Itzkan, Physical Review Letter, 78, 1997. 1667-1670; “Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics”, Christy L. Haynes and Richard P. Van Duyne, J. Phys. Chem. B 2001, 105, 5599-5611.
However, these publications do not provide an effective method to produce and package the non-contaminated nano-structured noble metal surface to achieve field applications of SERS and SERRS for trace chemical detection. Furthermore, none of these publications provide method to fabricate nano-structured materials with well-controlled nano array that have reduced and optimized dimensions of the nano-particles and reduced and optimized distances among these nano-particles on the surface to achieve scattering signal enhancement.
There are ever increasing demands to take advantage of the greatly improved nano-structured surface now provided by the invention as that disclosed in the co-pending Application so that Raman sensors can be practically implemented to effectively realize these applications that are urgently in demand.
Therefore, a need still exists in the art to provide practical configuration for conveniently implement the Raman sensors in applications to antiterrorism, forensic, medical diagnoses, disease preventions, industrial process monitoring, environmental cleaning up and monitoring, food, and drug quality control, etc.